This invention relates to an improved solid rocket engine.
Conventional solid rocket engines comprise a solid propellant, a case which defines the combustion chamber for the propellant, and an exhaust nozzle, as well as means for igniting the propellant. Research directed to each of the major components of rocket engines continues in efforts to reduce cost, reduce dead weight, and increase engine thrust.
The most severe heating of the hardware takes place at the exhaust nozzle. High-velocity gas at high temperature oxidizes, softens, wears and erodes the nozzle material. Metal nozzles, with or without protective coverings, may be used for short-duration burns. Ceramic nozzles have been successful for long periods of time. Carbon--carbon nozzles have also been successful.
One application for which nozzle research is considered important is the integral rocket-ramjet engine. Early prototypes of this type engine merely mounted a rocket engine in tandem with a ramjet engine. Current designs of integral rocket-ramjet engines employ a single combustion chamber. This chamber initially contains a solid rocket propellant. Following ignition and burning of the propellant, the chamber is converted for ramjet operation.
The two modes of operation, i.e., rocket mode and ramjet mode, require exhaust or thrust nozzles of different cross-sectional areas due to the difference of pressure, volume and velocity of the exhuast gases while operating under each mode. One manner of attaining this end is to provide a rocket nozzle which telescopes within the ramjet nozzle and is ejected at rocket burnout, providing a larger nozzle for ramjet operation. An example of this approach is disclosed by Platzek, U.S. Pat. No. 3,855,789.
While the telescoping, ejectable nozzle disclosed by Platzek provides a solution to the requirement for dual nozzles, it also introduces other problems, such as the ejected nozzle itself. In the case of air-launched vehicles, any ejecta is desirably avoided, because it is possible that the ejecta might fall directly in the path of the launching aircraft.
The nozzleless rocket motor was developed to replace the conventionally nozzled motor in a number of specialized applications. The nozzleless motor is less expensive, requires less insulation, eliminates the dead weight of a rocket nozzle, accepts more propellant in a given case volume and eliminates ejecta in integral rocket-ramjet systems. The nozzleless rocket motor comprises a major portion of main grain propellant and a minor portion of a slower burning nozzle propellant. The nozzle propellant is used to form a throat and to provide an expansion surface for the exhaust gases. As used herein, and in the claims the term "nozzleless" is intended to mean a solid rocket motor which does not comprise a separate nozzle.
In these nozzleless rocket motors it is desirable that the nozzle portion burn slow enough to hold up as a nozzle, yet fast enough to contribute to the overall thrust. If the burn rate of the nozzle propellant is too slow, diminution of the nozzle is determined by the erosive environment provided by upstream gases. If the burn rate of the nozzle propellant is too fast, i.e., greater than the minimum rate determined by the erosive upstream gases, the nozzle throat opens too quickly.
The main grain propellant has evolved from the black powder used in early rockets, through the double-base propellants such as those based on nitroglycerine and nitrocellulose, to the composite propellants of today which consist of crystalline. finely-ground oxidizer particles dispersed in a matrix of a fuel compound.
It is an object of the present invention to provide an improved nozzleless solid rocket motor comprising means for reducing erosive burning effects in the nozzle portion.
Other objects and advantages of the present invention will be apparent to those skilled in the art.